Abstract

We report on the measurement and analysis of the polarization state of second harmonic signals generated by starch granules, using a four-channel photon counting based Stokes-polarimeter. Various polarization parameters, such as the degree of polarization (DOP), the degree of linear polarization (DOLP), the degree of circular polarization (DOCP), and anisotropy are extracted from the 2D second harmonic Stokes images of starch granules. The concentric shell structure of a starch granule forms a natural photonic crystal structure. By integration over all the solid angle, it will allow very similar SHG quantum efficiency regardless of the angle or the states of incident polarization. Given type I phase matching and the concentric shell structure of a starch granule, one can easily infer the polarization states of the input beam from the resulting SH micrograph.

Experimental reconstructed 2D Stokes images of the SHG response from starch granules for (a) horizontally, (b) vertically, (c) right and (d) left circularly polarized illumination, respectively. White arrows in the leftmost images indicate the direction of polarization. The color scale shows the value of each Stokes parameter increasing from blue to red. A schematic model of a starch granule is shown in (f).

Experimental polarization-resolved 2D reconstructed DOP, DOLP, DOCP and polarization anisotropy images of SHG response from starch granule for the; (a) horizontal, (b) vertical, (c) right and (d) left circularly polarized polarization respectively. The direction of polarization is indicated by a white arrow in the images. The color scale shows the values of each parameter increases from blue to red.